For example, in an Ethernet (registered trademark) network, Ethernet switches (referred to hereinafter as a switch for simplicity) acting as multiple relay devices are connected in a ring shape to form a ring topology. In the ring topology, two ports of each switch are connected to ports of other switches to connect the multiple switches in the ring shape. The multiple switches and communication lines connecting the switches constitute a ring shape communication path allowing frame circulation. The ring shape communication path can be used as a two-way communication path through which each switch can perform transmission in both of a clockwise direction and an anticlockwise direction (for example, see Patent Literature 1).
Patent Literature 1: JP-2010-509825A